With the growing concern for global warming, the use of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) as refrigerant has been identified as having a negative impact on the environment. These chemicals have non-negligible ozone-depletion potential and/or global-warming potential.
As alternatives to CFCs and HCFCs, ammonia, hydrocarbons and CO2 are used as refrigerants. Although ammonia and hydrocarbons have negligible ozone-depletion potential and global-warming potential as does CO2, these refrigerants are highly flammable and therefore represent a risk to local safety. On the other hand, CO2 is environmentally benign and locally safe.